United Nations chief Ban Ki-moon said on Saturday that saving the lives of migrants stranded at sea in Southeast Asia should be a “top priority” as the region battles with an exodus of migrants fleeing persecution and poverty.

The UN secretary general said he hoped regional nations would tackle the “root causes” of the current exodus at an upcoming conference in Thailand later this month.

“But when people are drifting on the sea, how we can search and rescue them and provide life saving humanitarian assistance, that is a top priority at this time,” he told reporters during a visit to Hanoi.

Ban said he had been in recent discussions with regional leaders in Thailand, Malaysia and Burma and urged a “very clear addressing of the root causes of this issue, why people are fleeing”.

Ban’s comments come as Burma faces growing international pressure to address its treatment of the country’s 1.3 million Rohingya minority Muslims who mainly live in the country’s western Arakan State.

Ban also called on countries who receive migrants “not to send them back to a dangerous circumstance or situation”.

Thailand has organised a regional conference in Bangkok on 29 May to address the crisis.

Meanwhile, Indonesia has told Australia that most of the migrants stranded at sea in Southeast Asia are illegal labourers from Bangladesh, not oppressed Muslim Rohingya, according to Foreign Minister Julie Bishop in comments published on Saturday.

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Speaking to Australia’s The Weekend newspaper, Bishop said Indonesia estimated that only 30 to 40 percent of the thousands still stranded at sea were Rohingya.

“They [Indonesia] believe there are about 7,000 people at sea. They think about 30 to 40 percent are Rohingya, the rest are Bangladeshi; and they are not, in Indonesia’s words, asylum seekers, they are not refugees – they are illegal labourers. They’ve been promised or are seeking jobs in Malaysia,” Bishop said.

“They said the Rohingya have gone to Bangladesh and have mixed up with the Bangladeshis who are coming to Malaysia in particular for jobs,” she said, adding that Indonesia’s director-general of multilateral affairs, Hasan Kleib, had told her that on one vessel, Bangladeshis accounted for 400 of the 600 people onboard.

Rohingya in Burma are are frequently pejoratively referred to as ‘Bengalis’, a suggestion that they belong in Bangladesh. The 1.3 million Rohingya are not among the officially recognised ethnic groups of Burma, and are therefore denied citizenship, leaving them effectively stateless.

Burma has faced increasing international pressure to stem the exodus from its shores and deliver urgent humanitarian relief to thousands still trapped at sea.

Australia, which maintains a hardline policy of denying asylum seekers who arrive by boats resettlement and which turns back vessels when it can, has maintained its refusal to resettle any stranded migrants, saying to do so would encourage people smuggling.

“I will say or do nothing to encourage people to take to the sea in boats and any suggestion that there is some kind of special resettlement program here in Australia for people taking to the sea in boats just encourages people-smuggling,” Prime Minister Tony Abbott said on Friday.

“So it would be utterly irresponsible of me or anyone to suggest for a second that we will reward people for doing something so dangerous.”